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Last night, rapper B.o.B took to Twitter to enlighten his 2.29 million followers with a brief introduction to the Flat Earth theory.

https://twitter.com/bobatl/status/691439089543880704

The Flat Earth theory is exactly what it sounds like: a theory insisting that the Earth is flat (despite thousands of years of scientific evidence proving otherwise). Unlike most conspiracy theories born out of a disbelief or distrust of something put forth as fact, the Flat Earth theory harkens back to a time when people simply didn't have the tools available to investigate the world's actual shape.

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In 1849, English writer Samuel Birley Rowbotham gave birth to the modern Flat Earth movement with a 16-page pamphlet in which he argued that the Earth was actually a flat disk, centered around the North Pole and surrounded by Antarctica, which is actually a gargantuan wall of ice.

A diagram of a flat Earth surrounded by the Antarctic ice wall.

Though Rowbotham was not a trained Earth scientist, surveyor of the land, or astronomer, that did not stop him from performing a number of scientifically dubious experiments and publishing his work as fact during the late 19th century. Rowbotham (and B.o.B) famously pointed to his execution of the Bedford Level experiment as proof that the Earth was actually flat.

https://twitter.com/bobatl/status/691514326646022144

The Bedford Level experiment tested the idea of the Earth's curvature by placing three poles of equal length into the ground along a six-mile length on the Old Bedford River in Norfolk, England. The river was chosen because of its seeming flatness and straightness. When performed properly, the experiment would demonstrate that the pole located in the middle of the six-mile stretch was actually about three feet higher than either of the other two poles.

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When Rowbotham first performed his version of the experiment, he used a somewhat different method. Instead, Rowbotham opted to wade into the middle of the Bedford River, telescope in hand, as he watched a bow row away from him. If the Earth was actually curved, Rowbotham argued, then the top of the boat's mast should have begun to disappear the farther it got away from him. Rowbotham observed no such disappearance and published his findings in Zetetic Astronomy in 1849 using the pseudonym "Parallax."

Here's the thing about Rowbotham's experiment. He did it wrong. Or at the very least, he didn't quite understand what he was looking at.

In 1890 John Hampden, an ardent supporter of Rowbotham's theory, put forth a standing public wager that he could prove that the Earth was flat. Anyone who could disprove his and Rowbotham's beliefs would be awarded £500. Alfred Russel Wallace, a legitimate geographer and surveyor graciously accepted the offer and began to recreate the Bedford Level experiment.

In addition to relying on more than a telescope and his eyes to prove his point, Wallace included the crucial step of setting a sight line 13 feet above the water's surface so as to counter the distorting effects of atmospheric refraction.

As sunlight travels to the Earth's surface, it's refracted by the planet's atmosphere, which causes the bulk of light moving horizontally to bend downward at an angle matching the exact curvature of the Earth. This phenomenon can cause one to perceive the Earth as being flat. In the end, the bet's referee judged that Wallace had won. Hampden insisted that Wallace cheated and the two became embroiled in a very ugly, very public court battle.

Media coverage of the lawsuit between Hampden and Wallace after their bet.

Even though Rowbotham's theory had been debunked, his influenced proved to be stronger than any objective experimentation. In 1881, Rowbotham expanded upon Zetetic Astronomy and wrote The Earth Not a Globe Review, which would go on to play a pivotal role in the founding of the modern Flat Earth Society.

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Even if Wallace's demonstration proving that the basis of the Flat Earth Society's stance was faulty, there are plenty of other scientifically sound ways that we know that the Earth is spherical.

The Moon

Getty Images

A couple of times every year, the Earth finds itself situated between the Moon and the Sun. This is known as a Lunar eclipse. During a Lunar eclipse, the Earth is blocking the Sun's light from hitting the Moon, casting a shadow onto it.

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Because the Earth is a sphere, the shape of that shadow it casts is (spoiler alert) round. Often, Flat Earth believers point out that the Earth could be both flat and round, but when one remembers that the Earth is also spinning, that logic falls apart.

Editor's note: B.o.B. seems to take issue with the idea of the Earth spinning.

https://twitter.com/bobatl/status/691420171693469696

Ships and the horizon

This is another simple optical test that even the most non-scientifically minded person can conduct. When you stand on land and watch a boat go out to sea, not only is the boat "shrinking" because it's getting farther away, at some point you can also observe the object to be "sinking" as it moves along with the curvature of the Earth. This wouldn't happen on a flat planet.

Visibility of constellations

The farther you move away from the equator, the more difficult it is to observe the same constellations that are easy to view when you're close to the equator.

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This effect is caused by the change in field of view that occurs when you move along the surface of a curved object. After a certain point of moving along a sphere, that which was once directly overhead won't be visible because the object's curve prevents you from seeing at certain angles. This would not be the case on a flat plane.

Timezones

When it's 2 p.m. EST and bright and sunny in New York City, it's about 12:30 a.m. in New Delhi, India, well into the evening. Because of the Earth's spherical shape and its rotation around the sun, countries across the world gradually experience the phases of the day as their parts of the planet face the Sun and eventually turn away.

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If the Earth were flat and centered around the North Pole, the planet would never experience true night time, considering that the sun's rays would only have to reach across a flattened surface in order to illuminate the entire planet.

Live footage from the International Space Station

Even with all of the logical and scientific evidence pointing to the idea of a spherical Earth, many people still find it difficult to accept, given that it's nearly impossible to ever actually see the planet's curvature.

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B.o.B, for instance still couldn't see the curve when he was up in the air at the same height as Felix Baumgartner:

https://twitter.com/bobatl/status/691432090131247104

As impressive as Baumgartner's epic jump was, he was only about 24 miles above the Earth's surface. The International Space Station, on the other hand, is about 250 miles above the Earth, well into the planet's orbit. The view, in addition to being gorgeous, clearly demonstrates just what shape the Earth is.

That is, unless the government is manipulating the footage.